This invention relates to internal combustion engines and more particularly to two-cycle diesel engines wherein a positive displacement blower provides scavenging and charging air to the cylinders and an exhaust driven turbochargers is used to pressurize the air delivered to the blower, thereby increasing charge density in the cylinders for high output operation.
It is known in the art to provide a two-cycle diesel engine with a positive displacement charging pump such as a Roots blower for delivering air to an engine air box connecting with cylinder air inlet ports to positively scavenge and charge the cylinders. It is further known to increase the maximum output capability of such engines by providing an exhaust driven turbocharger arranged to deliver pressurized air to the inlet of the Roots blower during engine operation at sufficiently high loads. The operation of such air supply systems yields relatively high charging air temperatures which result in high cylinder combustion and engine components temperatures.
In some such engines these temperatures have been reduced by providing an aftercooling heat exchanger between the turbocharger and the cylinders to remove some of the heat of compression from the charging air. Such arrangements have the further advantage of increasing the cylinder charge density, thereby permitting increased power output to be obtained from the engine.
However, in engines incorporating positive displacement charging pumps, such as the pistons of four-cycle engines or the rotary blower of some two-cycle engines, cooling of the pump inlet results in increasing the mass of air pumped through the engine. The additional airflow combined with the added restriction of the cooler in the system tends to increase system pumping losses while at the same time the turbocompressor operating line moves into a less efficient operating range under the increased flow conditions.
A published report in SAE Transactions, Volume 67, 1959, pages 411-412 indicates some consideration has been given to the inherent cooling capacity of the water cooled air box walls of a two-cycle diesel engine. In addition, the use of finned water tubes in the air box to obtain further cooling has been tried with limited success. However, it has been considered that such devices would be rendered less effective in time due to sludging or collection of carbon and other deposits which would plug cooling devices located in the air box environment.